A tremendous variety of devices used today rely on actuators of one sort or another to convert electrical energy to mechanical energy. Conversely, many power generation applications operate by converting mechanical action into electrical energy. Employed to harvest mechanical energy in this fashion, the same type of device may be referred to as a generator. Likewise, when the structure is employed to convert physical stimulus such as vibration or pressure into an electrical signal for measurement purposes, it may be characterized as a sensor. Yet, the term “transducer” may be used to generically refer to any of the devices.
A number of design considerations favor the selection and use of advanced dielectric elastomer materials, also referred to as “electroactive polymers”, for the fabrication of transducers. These considerations include potential force, power density, power conversion/consumption, size, weight, cost, response time, duty cycle, service requirements, environmental impact, etc. As such, in many applications, electroactive polymer technology offers an ideal replacement for piezoelectric, shape-memory alloy and electromagnetic devices such as motors and solenoids.
An electroactive polymer transducer comprises two electrodes having deformable characteristics and separated by a thin elastomeric dielectric material. When a voltage difference is applied to the electrodes, the oppositely charged electrodes attract each other thereby compressing the polymer dielectric layer therebetween. As the electrodes are pulled closer together, the dielectric polymer film becomes thinner (the Z-axis component contracts) as it expands in the planar directions (along the X- and Y-axes), i.e., the displacement of the film is in-plane. The electroactive polymer film may also be configured to produce movement in a direction orthogonal to the film structure (along the Z-axis), i.e., the displacement of the film is out-of-plane. For example, U.S. Pat. No. 7,567,681 discloses electroactive polymer film constructs which provide such out-of-plane displacement—also referred to as surface deformation or as thickness mode deflection.
The material and physical properties of the electroactive polymer film may be varied and controlled to customize the deformation undergone by the transducer. More specifically, factors such as the relative elasticity between the polymer film and the electrode material, the relative thickness between the polymer film and electrode material and/or the varying thickness of the polymer film and/or electrode material, the physical pattern of the polymer film and/or electrode material (to provide localized active and inactive areas), the tension or pre-strain placed on the electroactive polymer film as a whole, and the amount of voltage applied to or capacitance induced upon the film may be controlled and varied to customize the features of the film when in an active mode.
Numerous applications exist that benefit from the advantages provided by such electroactive polymer films whether using the film alone or using it in an electroactive polymer actuator. One of the many applications involves the use of electroactive polymer transducers as actuators to produce haptic, tactile, vibrational feedback (the communication of information to a user through forces applied to the user's body), and the like, in user interface devices. There are many known user interface devices which employ such feedback, typically in response to a force initiated by the user. Examples of user interface devices that may employ such feedback include keyboards, keypads, game controller, remote control, touch screens, computer mice, trackballs, stylus sticks, joysticks, etc. The user interface surface can comprise any surface that a user manipulates, engages, and/or observes regarding feedback or information from the device. Examples of such interface surfaces include, but are not limited to, a key (e.g., keys on a keyboard), a game pad or buttons, a display screen, etc.
Use of electroactive polymer materials in consumer electronic media devices as well as the numerous other commercial and consumer applications highlights the need to increase production volume while maintaining precision and consistency of the films. There is also a need to ensure the safety of the consumer during use of electroactive polymer devices which may be operated at high operating voltages.
Conventional rolled dielectric elastomer transducer based cylindrical actuators are desirable because a cylindrical shape is functional and familiar. It matches many mechanical components, such as, for example, solenoids, air cylinders, shock absorbers, etc. so mounting hardware is readily available, for example, the clevis, the ball joint, and the threaded rod. Engineers' familiarity with cylindrical actuators simplifies their efforts to integrate them in new designs. Nevertheless, hollow, rolled dielectric elastomer tubes and tubes with an internal spring, called “spring rolls” have some drawbacks. Empty space inside the tube is wasted, making the transducer larger than strictly necessary. Also, accumulated tension from winding the outer layers of the tube tends to buckle and collapse the tube. In a tubular roll made with a highly prestrained acrylic dielectric, this imposed a practical limit of only a few turns per transducer.
Multilayer stacked actuators similarly eliminate wasted empty volume to maximize the density of active material. They may be particularly desired in applications where they are mounted onto a flat surface.
The present disclosure provides dielectric elastomer compliant actuators comprising dielectric elastomer transducers provided in various packages and configurations for interfacing with devices and users. Such compliant actuators may be integrated into various products and may be configured as active buttons and display surfaces for custom button clicks, navigation cues, and the like. Soft, shielded actuators may be projected through hard cases and housing of products such as smartphones, game consoles, pad computers, and the like.